JP2018064186A - Transmission device and reception device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform transmission that hardly makes a bit error and improve the effect of frequency interleave regarding a particular bit stream when a plurality of bit streams are transmitted.SOLUTION: When a transmission device for modulating and transmitting a plurality of series of bit streams maps M bits as one signal point, where M is an integer of two or more, it divides the M bits into a plurality of groups, and allocates different bit streams to the respective groups. A reception device receiving a modulated signal generated by mapping a plurality of series of bit streams to one signal point de-maps the signal point, and separates obtained data by the bit into the plurality of series of bit streams.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a transmission device and a reception device, and more particularly, to a transmission device and a reception device that transmit a plurality of bit streams having different noise immunity on the same channel.

  In recent years, needs for video distribution services have been diversified, and video distribution assuming a plurality of reception modes has also been performed. For example, in current terrestrial television broadcasting, hierarchical transmission technology is used, and a plurality of services having different noise resistance and image quality are provided in the same channel. Specifically, in the current digital terrestrial broadcasting, the frequency band of one channel (about 6 MHz) is divided into 13 bands (segments), and one segment in the center of the transmission band is divided into mobile receiving terminals (mobile terminals) ) And a service that transmits strong noise-tolerant video (so-called one-segment broadcasting), and other 12 segments for fixed reception terminals (home TVs, etc.) A service for transmitting high-quality video (such as high-definition broadcasting) is provided (Non-Patent Document 1). As described above, a technique for transmitting different bit streams in one channel while realizing different noise immunity is attracting attention.

  FIG. 4 is a block diagram illustrating an example of a transmission apparatus and a reception apparatus that perform hierarchical transmission of a plurality of bit streams using OFDM (Orthogonal Frequency Division Multiplexing) transmission by conventional mapping processing. The input bit stream has two layers, and bit stream 1 with high noise resistance (for example, for mobile reception terminals) is called layer A, and bit stream 2 with low noise resistance but high image quality is called layer B. The data of the A layer bit stream is represented by a, and the data of the B layer bit stream is represented by b.

  4A includes an interface unit 11, a layer division unit 12, error correction coding units 13 and 14, mapping units 15 and 16, an OFDM frame configuration unit 17, and an IFFT (Inverse Fast Fourier Transform) unit. 18, an orthogonal modulation unit 19 is provided, and a signal obtained by synthesizing two bit streams is input, and an OFDM-modulated transmission signal is output.

  The interface unit 11 receives a digitized input signal (for example, a bit stream of two layers) such as video / audio, and performs interface processing suitable for subsequent processing on this data string. For example, when the error correction code used in the European terrestrial digital broadcasting transmission standard DVB-T2 (Non-Patent Document 2) is used in the subsequent error correction coding process, an LDPC (low-density) code length of 64800 bits is used. (parity-check code) interface processing such as blocking processing for encoding is performed.

  The hierarchy division unit 12 divides the data received from the interface unit 11 into respective hierarchy data. Then, the A layer bit data is output to the error correction encoding unit 13, and the B layer bit data is output to the error correction encoding unit 14.

  The error correction coding units 13 and 14 apply error correction coding processing to the input data (data block or the like) received from the layer division unit 12 at a predetermined coding rate. Here, the error correction encoding unit 13 performs error correction encoding processing on the data of the A layer, and outputs the corrected data string to the mapping unit 15. Similarly, the error correction encoding unit 14 performs error correction encoding processing on the data of the B layer, and outputs the corrected data string to the mapping unit 16. Specifically, an error correction code is added to the block data having a predetermined number of bits to generate an error correction block having a predetermined length. As the error correction code, for example, an LDPC code is preferably used, but another error correction code may be used. As will be described later, when an LDPC code is used, LLR (Logarithm of Likelihood Ratio) is calculated as a ratio of plausibility of whether a bit is 0 or 1 in the demapping process on the receiving side. Thereafter, error correction decoding can be performed using LLR which is likelihood information.

The mapping units 15 and 16 are defined as complex numbers on the IQ plane, that is, ideally defined on the IQ plane, with m bits (m is an integer of 1 or more) of the bit string to which the error correction coding process is applied as one unit. The process of mapping to the coordinates of the correct signal point is performed. Here, when 1024QAM (Quadrature Amplitude Modulation) is applied by the mapping units 15 and 16, the bit stream subjected to error correction coding is mapped in units of 10 bits. The input bits are represented as a [0], a [1], ..., a [9] (where a [*] ∈ (0,1)), and the output of the mapping is (I, Q) It is expressed as a complex number (where I and Q are real numbers). For example, in the European cable television transmission standard DVB-C2 (Non-Patent Document 3), 1024QAM is adopted, and input bits (a [0], a [1], a [2], a [3 ], a [4], a [5], a [6], a [7], a [8], a [9]) = (0, 0, 0, 0, 0, 0, 0, 0, 0,0) is mapped to output I / Q = (31/682 ^1/2 , 31/682 ^1/2 ).

  The mapping unit 15 maps the 10-bit data string (a [0] -a [9]) of the A layer input from the error correction coding unit 13, and sets the resulting I / Q data as an OFDM frame structure To the unit 17. Similarly, the mapping unit 16 maps the B-layer 10-bit data string (b [0] -b [9]) input from the error correction encoding unit 14 and outputs the resulting I / Q data. The data is output to the OFDM frame configuration unit 17. Note that the mapping processing (carrier modulation scheme) of the mapping units 15 and 16 may be different. For example, in the current terrestrial digital broadcasting, data for one-segment service is modulated with QPSK (Quadrature Phase Shift Keying): coding rate 2/3, and data for high-vision service is 64QAM: coding rate 3/4. Modulated. As described above, the modulation scheme of the mapping unit 15 can be a modulation scheme having higher noise resistance than the mapping unit 16.

  The OFDM frame configuration unit 17 arranges the symbols (I / Q data) formed by the mapping units 15 and 16 on a plurality of subcarriers (frequency axis) and the time axis to configure an OFDM frame. The OFDM frame configuration unit generates an OFDM frame by using the data carrier symbols of the A layer and the B layer together. Although not shown, a pilot signal (SP signal, CP signal) or a TMCC (Transmission and Multiplexing Configuration and Control) signal may be arranged in the frame as necessary. In the current terrestrial digital broadcasting ISDB-T (Integrated Services Digital Broadcasting-Terrestrial) system in Japan, the OFDM frame configuration unit performs hierarchical transmission by frequency division multiplexing. For example, the data carrier symbol of the A layer can be arranged in the center frequency region of the transmission band, and the data carrier symbol of the B layer can be arranged in the frequency region on both sides of the A layer. In European DVB-T (Digital Video Broadcasting-Terrestrial) 2, the OFDM frame configuration unit performs hierarchical transmission by time division multiplexing.

  The IFFT unit 18 receives an OFDM frame signal from the OFDM frame configuration unit 17 and performs IFFT processing on the modulated signal to convert the frequency domain signal into a time domain signal. Then, IFFT unit 18 outputs the modulated signal converted into the time domain signal to quadrature modulation unit 19.

  Based on the signal output from the IFFT unit 18, the orthogonal modulation unit 19 performs orthogonal modulation on each symbol to generate a transmission signal. Thereafter, the transmission device 10 converts the orthogonally modulated transmission signal into a radio frequency, performs necessary amplification, and transmits the signal to the reception device using one or a plurality of antennas.

  Next, a receiving apparatus that performs conventional hierarchical transmission will be described with reference to FIG. The receiving device 30 includes an orthogonal demodulation unit 31, an FFT (Fast Fourier Transform) unit 32, a data symbol extraction unit 33, demapping units 34 and 35, error correction decoding units 36 and 37, a layer synthesis unit 38, and an interface unit 39. The received signal modulated by OFDM is input, and the combined signal of the bit stream 1 and the bit stream 2 is decoded and output.

  A radio signal sent from the transmission side is received by one or more antennas, performs a necessary process such as frequency conversion of a radio frequency signal to a predetermined intermediate frequency, and is input to the quadrature demodulator 31 as a received signal. Is done. The orthogonal demodulator 31 performs orthogonal demodulation on the input received signal. Further, signal processing necessary for subsequent FFT processing, such as removal of the guard interval, is performed and output to the FFT unit 32.

  The FFT unit 32 performs FFT processing on the quadrature demodulated signal and converts the time domain signal into a frequency domain signal. Then, the FFT unit 32 outputs the signal converted to the frequency domain to the data symbol extraction unit 33.

  The data symbol extraction unit 33 extracts necessary data signals (data symbols), TMCC signals, pilot signals (SP signals, CP signals), etc., from the signals (OFDM frame signals) converted into the frequency domain by the FFT unit 32. To do. The obtained data symbols (I / Q data) are separated according to the hierarchy, the data symbols of the A layer are output to the demapping unit 34, and the data symbols of the B layer are output to the demapping unit 35.

  The demapping unit 34 performs demapping to demodulate the data of the A layer, and the demapping unit 35 performs demapping to demodulate the data of the B layer. The demapping here is a process for obtaining a likelihood corresponding to each bit of a bit string (for example, 10 bits for 1024QAM) represented by the received symbol from the received symbol (received signal) mapped on the IQ plane. That is, the “demapping process” in the present invention corresponds to an operation for calculating an LLR (log likelihood ratio) used for error correction decoding. The LLRs (α [0], α [1],..., Α [9]) of each bit calculated by the demapping unit 34 are output to the error correction decoding unit 36 and are calculated by the demapping unit 35. The bit LLRs (β [0], β [1],..., Β [9]) are output to the error correction decoding unit 37.

  The error correction decoding unit 36 performs error correction decoding processing using the LLR (α [0] −α [9]) corresponding to the bit string of the A layer output from the demapping unit 34. Further, the error correction decoding unit 37 performs error correction decoding processing using the LLR (β [0] −β [9]) corresponding to the B-layer bit string output from the demapping unit 35. The error-corrected bit string is output to the layer synthesis unit 38.

  The layer synthesis unit 38 combines the error-corrected A layer data and B layer data, and generates a multiplexed data string.

  The interface unit 39 performs necessary data processing on the data output from the layer combining unit 38 and multiplexed by combining the two layers, and a bit stream 1+ that is a data signal such as video / audio. The re-multiplexed signal of the bit stream 2 is output.

  The transmitting device and the receiving device in FIG. 4 can transmit bit streams of two layers having different noise immunity by changing the coding rate of error correction codes used in the A layer and the B layer and the number of mapping signal points. it can.

"Digital Terrestrial Television Broadcasting Transmission System" Standard, ARIB STD-B31, The Japan Radio Industry Association, <URL: http://www.arib.or.jp/english/html/overview/doc/2- STD-B31v1_9.pdf> “Digital Video Broadcasting (DVB); Frame structure channel coding and modulation for a second generation digital terrestrial television broadcasting system (DVB-T2)”, <URL: https://www.dvb.org/standards/dvb-t2> “Digital Video Broadcasting (DVB); Frame structure channel coding and modulation for a second generation digital transmission system for cable systems (DVB-C2)”, <URL: https://www.dvb.org/standards/dvb-c2>

  In conventional hierarchical transmission, each bit stream is mapped independently, and then both are integrated in an OFDM frame. However, when mapping a single bitstream to an IQ value in units of M (M is an integer of 2 or more) bits as in the conventional mapping process, an error-prone bit in M bits, When bits that are hard to occur are mixed, it is one of the factors that degrade the bit error rate characteristics.

  FIG. 5 shows an error rate characteristic of each bit in a Gaussian noise environment of 1024QAM transmission. The bit error rate characteristics shown in FIG. 5 are measured by using the DVPC-T2 LDPC code (code length 64800, coding rate R = 4/5) as an error correction code and the system shown in FIG.

  First, the measurement system in FIG. 6 will be briefly described. The transmission apparatus in FIG. 6A is one-layer transmission in which one system of bit stream 1 is input as an input signal, and the mapping process determines the coordinates of signal points using 1024QAM and the Gray code on the IQ plane.

  The input bit stream 1 is subjected to interface processing suitable for error correction coding at the interface unit 11, and the LDPC coding processing is performed at the error correction coding unit 13. When 1024QAM is applied, the error correction coded bitstream is mapped on the IQ plane by the mapping unit 15 in units of 10 bits (a [0] -a [9]). A signal based on the obtained I / Q data is orthogonally modulated by the orthogonal modulation unit 19 and output as a transmission signal.

  The receiving apparatus in FIG. 6B performs demodulation / decoding processing corresponding to the transmitting apparatus. The received signal orthogonally demodulated by the orthogonal demodulator 31 is subjected to demapping processing (calculating the LLR of each bit based on the received signal on the IQ plane) by the demapping unit 34, and the LLR (α [0]) of each bit is calculated. −α [9]), the error correction decoding unit 36 performs error correction decoding processing (LDPC decoding processing). Thereafter, the bit stream 1 is output via the interface unit 39.

  FIG. 5 shows the error rate characteristics of each bit of 1024QAM measured by such a measurement system as a horizontal axis CNR (Carrier-Noise Ratio) and a vertical axis BER (Bit Error Rate). Show. From FIG. 5, it can be seen that there is a difference in the error rate characteristics of each bit, and the 10-bit average bit error rate characteristics (thick solid line) constituting 1024QAM are close to the characteristics of bits that are prone to error.

  Accordingly, an object of the present invention made in view of the above-described problems is to provide a transmission apparatus capable of performing transmission with which a bit error hardly occurs with respect to a specific bit stream when transmitting a plurality of bit streams. To provide a receiving apparatus.

  In order to solve the above-described problem, a transmitting apparatus according to the present invention modulates and transmits a plurality of bitstreams when mapping M (M is an integer of 2 or more) bits as one signal point. , A layer mapping unit that divides M bits into a plurality of groups and assigns different bit streams to each group, and the layer mapping unit extracts Na (Na is an integer of 1 or more) from data based on the first stream of bit streams. A first bit extracting unit for extracting bits, a second bit extracting unit for extracting Nb (Nb is an integer of 1 or more) bits from data based on a second stream of bit streams, the Na bit, and the Nb bit And a mapping unit that maps the synthesized bits on IQ coordinates as one signal point. And wherein the door.

  The transmitting apparatus may divide the M bits into a plurality of groups on the basis of the likelihood of bit errors.

  In addition, the transmission apparatus includes a first error correction coding unit that performs error correction coding processing on the first stream of bit streams, and second error correction coding that performs error correction coding processing on the second stream of bit streams. A bit stream that has been subjected to error correction coding processing is preferably input to the layer mapping unit.

  In the transmission apparatus, it is preferable that the first error correction encoding unit and the second error correction encoding unit perform different encoding processes.

  Further, it is preferable that the transmission apparatus performs OFDM modulation by arranging signal points (data symbols) generated by the layer mapping unit on a frequency axis and a time axis.

  In order to solve the above problems, a receiving apparatus according to the present invention obtains a signal obtained by demapping the signal points in a receiving apparatus that receives a modulated signal by mapping a plurality of bitstreams to one signal point. A hierarchical demapping unit that separates the bit-specific data into the multiple-sequence bitstreams, wherein the multiple-sequence bitstreams are subjected to error correction encoding processing before mapping, and the hierarchical demapping unit includes: A demapping unit for demapping signal points to obtain the likelihood of each bit, and a likelihood separating unit for separating the likelihood of each bit into the plurality of bit streams, and for each bit stream of each sequence An error correction decoding process is performed based on the likelihood.

  According to the transmission device and the reception device of the present invention, when transmitting a plurality of bit streams, by using bits that are unlikely to generate an error, it is possible to perform transmission that does not easily generate a bit error for a specific bit stream. it can.

It is a block diagram which shows an example of the transmitter which performs the hierarchical transmission of this invention, and a receiver. It is a block diagram which shows an example of the hierarchy mapping part in this invention. It is a block diagram which shows an example of the hierarchy demapping part in this invention. It is a block diagram which shows an example of the transmitter and receiver which perform the conventional hierarchical transmission. It is a figure which shows the error rate characteristic of each bit in the Gaussian noise environment of 1024QAM transmission. It is a block diagram of the system | strain (transmission / reception apparatus) which measures the error rate characteristic of each bit.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows an example of a transmission apparatus and a reception apparatus that perform hierarchical transmission as an embodiment of the present invention. FIG. 1A is a block diagram illustrating an example of a transmission apparatus that performs two-layer transmission using OFDM transmission, and FIG. 1B illustrates a reception apparatus that receives a signal of two-layer transmission. It is a block diagram which shows an example. Here, a transmission / reception apparatus using OFDM transmission will be described as an example. However, OFDM transmission is not an essential configuration for implementing the present invention.

  Hierarchical transmission is made up of two layers, and as in FIG. 4, bit stream 1 requiring high noise resistance is A layer, bit stream 2 requiring higher image quality than noise resistance is B layer, and bit of A layer The data of the stream is a, and the bit stream data of the B layer is b. For example, it is assumed that the bit stream 1 is a video signal for high-definition broadcasting and the bit stream 2 is a video signal for super high-definition broadcasting (8K: 7680 × 4320 pixels). Note that the hierarchy is not limited to two hierarchies, and the present invention can be applied to any multilayer hierarchy.

  The transmission apparatus 100 includes an interface unit 11, a layer division unit 12, error correction coding units 13 and 14, a layer mapping unit 20, an OFDM frame configuration unit 17, an IFFT unit 18, and an orthogonal modulation unit 19, and a plurality of bit streams are included. A transmission signal that is input and modulated from a plurality of bit streams into one data symbol (signal point) is output. Among these, the blocks other than the hierarchy mapping unit 20 are substantially the same as the configuration of FIG.

  The interface unit 11 receives a digitized input signal such as video / audio (for example, a signal obtained by remultiplexing a plurality of bitstreams of bitstream 1 + bitstream 2) using, for example, one cable, The input signal is subjected to necessary data processing such as block processing for dividing the input signal into blocks of an appropriate size in the subsequent error correction encoding processing.

  The hierarchy division unit 12 divides the data received from the interface unit 11 into respective hierarchy data. Then, the A layer bit data is output to the error correction encoding unit 13, and the B layer bit data is output to the error correction encoding unit 14.

  In the transmission apparatus 100, the interface unit 11 receives the re-multiplexed signal of the bit stream 1 + the bit stream 2, and then divides the signal into two hierarchical data by the hierarchical division unit 12. It is not necessary in the present invention to multiplex two hierarchical data (bitstream) into one input. For example, layer A bit stream 1 and layer B bit stream 2 are separately separated and input to the transmission apparatus, and each bit stream is input to the error correction encoders 13 and 14 via the corresponding interface units, respectively. You may do it.

  The error correction coding units 13 and 14 apply error correction coding processing to the input data (data block or the like) received from the layer division unit 12 at a predetermined coding rate. The error correction encoding unit 13 performs a predetermined error correction encoding process on the data of the A layer, and outputs the corrected data string to the layer mapping unit 20. Further, the error correction coding unit 14 performs error correction coding processing on the data of the B layer, and outputs the corrected data string to the layer mapping unit 20 in the same manner. In the figure, from the error correction encoding unit 13, the processed data string is divided into two bits a [0] -a [1] and output to the hierarchy mapping unit 20, and the error correction encoding unit 14 performs processing. The completed data string is divided into 8 bits of b [0] -b [7] and output to the layer mapping unit 20, but this number of bits is an example, and the work of dividing the data string into predetermined bits is The hierarchy mapping unit 20 may perform this.

  As the error correction code, for example, an LDPC code is preferably used, but another error correction code may be used. In addition, the error correction encoding unit 13 performs error correction encoding processing of both the encoding units 13 and 14, such as using an error correction code having a lower encoding rate (strong against errors) than the error correction encoding unit 14. May be different. In the present invention, the error correction coding process is not essential and does not depend on the presence or absence of the error correction code and the type of error correction code.

  The hierarchy mapping unit 20 uses 2 bits from the A hierarchy (a [0], a [1]) and 8 bits from the B hierarchy (b [0], b [1], ..., b [7]). In addition, 10-bit data is created, and this data is mapped by a predetermined modulation method (eg, 1024QAM) to obtain signal point data (I / Q).

FIG. 2 is a block diagram showing an example of the hierarchy mapping unit 20 in the present invention. Layer mapping unit 20, and N _A bit extraction section 21, and N _B-bit extractor 22, a bit combining unit 23, and a mapping unit 24.

The N _A bit extraction unit 21 is a data sequence of the A layer, here, a signal sequence (a [0], a [1], a [3] output from the error correction encoding unit 13 and output of the A layer. ],..., N _A bits (a [0], a [1],..., _A [N _A −1]) are extracted. Further, N _B bit extraction unit 22, data strings of the B layer, wherein the correction coded signal sequence of the B-layer which is output from the error correcting coding section 13 (b [0], b [ 1], b [3], ..., a), N _B bits (b [0], b [ 1], ..., b [N B -1]) to extract. Here, N _A-bit and N _B bits ratio, respectively and the data amount of the ratio of A-layer and B-layer, of the data mapped to one signal point, considering hardly occurs bits like the error Can be determined.

Bit combining unit 23 is bit input from N _A bit extraction section 21-bit and N _B bit extraction section 22 from which the N _A + N _B = N _C bits c [0], c [1 ] ,..., C [N _c −1], and outputs to the mapping unit 24 following the subsequent stage. It should be noted that when combining the bits of the A layer and the bits from the B layer, the data of the A layer that requires high noise resistance is assigned to a group of bits that are unlikely to cause an error in the subsequent mapping process, and an error is likely to occur. It is desirable to combine bits so that B-layer data is assigned to a group of bits.

Mapping unit 24, the N _C bits of data combined by the bit combining unit 23 maps the IQ plane by a predetermined modulation scheme, and outputs the data symbols (I / Q). In mapping, a non-uniform constellation can be used as necessary.

  The OFDM frame configuration unit 17 arranges the symbols (I / Q) formed by the mapping unit 20 on a plurality of subcarriers (frequency axis) and the time axis to configure an OFDM frame. Note that since the layer mapping unit 20 outputs symbols including data of the A layer and the B layer, an OFDM frame is generated using frequency interleaving or the like for the symbols. However, in the present invention, performing OFDM transmission is not an essential requirement, and the I / Q data output from the layer mapping unit 20 may be transmitted by a single carrier transmission signal.

  The IFFT unit 18 performs IFFT processing on the OFDM frame signal from the OFDM frame configuration unit 17 and converts the signal in the frequency domain into a signal in the time domain.

  Based on the signal output from the IFFT unit 18, the orthogonal modulation unit 19 performs orthogonal modulation on each symbol to generate a transmission signal. Thereafter, the transmission device 10 converts the orthogonally modulated transmission signal into a radio frequency, performs necessary amplification, and transmits the signal to the reception device 200 using one or a plurality of antennas.

  Next, a receiving apparatus that performs hierarchical transmission according to the present invention will be described. FIG. 1B is a block diagram illustrating an example of a receiving apparatus that receives a signal of two-layer transmission generated by the transmitting apparatus of the present invention.

  The receiving apparatus 200 includes an orthogonal demodulation unit 31, an FFT unit 32, a data symbol extraction unit 33, a layer demapping unit 40, error correction decoding units 36 and 37, a layer synthesis unit 38, and an interface unit 39, and a plurality of bitstreams. A received signal modulated into one data symbol (signal point) is received, and a plurality of bit streams are decoded and output. Among these, the blocks other than the hierarchy demapping unit 40 are almost the same as the configuration of FIG.

  A radio signal sent from the transmission side is received by one or more antennas, performs a necessary process such as frequency conversion of a radio frequency signal to a predetermined intermediate frequency, and is input to the quadrature demodulator 31 as a received signal. Is done. The orthogonal demodulator 31 performs orthogonal demodulation on the input received signal. Note that the signal received by the receiving apparatus 200 is a modulated signal generated by the transmitting apparatus 100 and including a plurality of series of bit streams in one data symbol.

  The FFT unit 32 performs FFT processing on the quadrature demodulated signal and converts the time domain signal into a frequency domain signal.

  The data symbol extraction unit 33 generates a data symbol, TMCC signal, pilot signal (SP signal, CP signal), etc. necessary for decoding the bit stream from the signal (OFDM frame signal) converted into the frequency domain by the FFT unit 32. Extract. The extracted pilot signal is used for transmission path estimation, and parameter information necessary for demodulation is obtained from the TMCC signal. The obtained data symbol (I / Q data) is output to the hierarchical demapping unit 40.

  The layer demapping unit 40 demaps the data symbol (received signal) input from the data symbol extraction unit 33, and the likelihood (α [0], α [1]) corresponding to 2 bits of the A layer, Likelihood (β [0], β [1],..., Β [7]) corresponding to 8 bits of the B layer is obtained, and information on this likelihood (LLR) is sent to the error correction decoding units 36 and 37, respectively. Output.

  FIG. 3 is a block diagram showing an example of the hierarchy demapping unit 40 in the present invention. The hierarchy demapping unit 40 includes a demapping unit 41 and a likelihood separating unit 42.

The demapping unit 41 performs N _c bit demapping from the I / Q data of the data symbol (received signal) input from the data symbol extracting unit 33, and the likelihoods γ [0], γ [1],. γ [N _c −1] is obtained and output to the likelihood separation unit 42. This likelihood can be used as an LLR (log likelihood ratio) of the LDPC decoding process in the subsequent error correction decoding process.

The likelihood separation unit 42 uses the transmitted likelihoods γ [0], γ [1],..., Γ [N _c −1] as bits (a [0], a [1] ,..., _A [N _A -1]) and the likelihood α [0], α [1],..., Α [N _A -1] and the bits (b [0], b [ 1],..., B [N _B -1]) are separated into likelihoods β [0], β [1],..., Β [N _B -1], and the error correction decoding units 36, To 37.

  Here, in the layer demapping unit 40, the likelihood (LLR) corresponding to each bit of each layer is obtained. However, when the error correction coding process is not performed on the transmission signal, or the LDPC coding is performed. When not used, general carrier demodulation processing may be performed as demapping processing to obtain a bit string corresponding to a data symbol (received signal).

The error correction decoding unit 36 accumulates the likelihood α [0], α [1],..., Α [N _A −1] corresponding to the bit string of the A layer output from the layer demapping unit 40, and has a predetermined value. When data corresponding to the error correction block is accumulated, an error correction decoding process (for example, an LDPC decoding process) is performed using the data as an LLR. Further, the error correction decoding unit 37 accumulates the likelihoods β [0], β [1],..., Β [N _B −1] corresponding to the bit string of the B layer output from the layer demapping unit 40, When data corresponding to a predetermined error correction block is accumulated, this is used as an LLR to perform error correction decoding processing (for example, LDPC decoding processing). The error-corrected bit string is output to the layer synthesis unit 38.

  The layer synthesis unit 38 combines the error-corrected A layer data and B layer data, and generates a multiplexed data string.

  The interface unit 39 performs necessary data processing on the data output from the layer combining unit 38 and multiplexed by combining the two layers, and the re-multiplexed signal of the bit stream 1 + the bit stream 2 Is output.

  In the present invention, it is not necessary in the present invention to multiplex bit stream 1 and bit stream 2. For example, the output data of the error correction decoding units 36 and 37 may be processed independently via the interface unit, and the A layer bit stream 1 and the B layer bit stream 2 may be separately separated and output. .

  Referring to FIG. 5, it can be seen that the bit error rate characteristics of the upper 2 bits (s0, s1) among the mapped bits are good. In the present embodiment, when the same error correction code is applied to the A layer and the B layer, transmission with high noise resistance can be realized by transmitting the bit stream of the A layer using only the upper 2 bits. In addition, since it is possible to change the strength (coding rate) of the error correction code in the A layer and the B layer, by using an error correction code with a low coding rate in the A layer, stronger noise resistance can be achieved. realizable.

  In the present invention, the OFDM modulation scheme is not an essential configuration. However, when a plurality of frequency carriers are used by OFDM modulation, a plurality of bit streams can be transmitted using carriers in all bands as described above. Higher frequency interleaving effect can be obtained and transmission characteristics can be improved.

  Heretofore, the A layer and the B layer have been described as different bit streams having different noise immunity, but the present invention can be applied to various layer transmissions. For example, when one video is encoded into video data including basic layer data L0, first layer data L1, and second layer data L2 by hierarchical encoding (scalable encoding), and only L0 is decoded, low quality, L0 When L1 is decoded, it can be used for an encoded transmission method in which medium quality is obtained, and when all video data of L0 to L2 is decoded, high quality decoded video is obtained. At this time, it is preferable to assign the basic layer data L0 to a bit that is less prone to error.

  Although the above embodiment has been described as a representative example, it will be apparent to those skilled in the art that many changes and substitutions can be made within the spirit and scope of the invention. Therefore, the present invention should not be construed as being limited by the above-described embodiments, and various modifications and changes can be made without departing from the scope of the claims. For example, a plurality of constituent blocks described in the embodiments can be combined into one, or one constituent block can be divided.

10 transmitting apparatus 11 the interface unit 12 hierarchically dividing unit 13 error-correction coding unit 15, 16 mapping unit 17 OFDM frame configuration section 18 IFFT section 19 quadrature modulator 20 layer mapping unit 21 N _A bit extraction section 22 N _B bits extracted Unit 23 bit synthesis unit 24 mapping unit 30 receiving device 31 orthogonal demodulation unit 32 FFT unit 33 data symbol extraction unit 34, 35 demapping unit 36, 37 error correction decoding unit 38 layer synthesis unit 39 interface unit 40 layer demapping unit 41 Mapping unit 42 Likelihood separation unit 100 Transmitting device 200 Receiving device

Claims (6)

In a transmission device that modulates and transmits a plurality of bitstreams,
When mapping M (M is an integer of 2 or more) bits as one signal point, a hierarchical mapping unit that divides M bits into a plurality of groups and assigns different bit streams to each group,
The hierarchical mapping unit includes a first bit extracting unit that extracts Na (Na is an integer of 1 or more) bits from data based on a first stream of bit streams;
A second bit extraction unit that extracts Nb (Nb is an integer of 1 or more) bits from data based on the second stream of bit streams;
A bit combiner for combining the Na bit and the Nb bit;
A transmission apparatus comprising: a mapping unit that maps the bits synthesized by the bit synthesis unit on IQ coordinates as one signal point. The transmission apparatus according to claim 1,
The transmitting apparatus according to claim 1, wherein the M bits are divided into a plurality of groups based on the likelihood of bit errors. The transmission apparatus according to claim 1 or 2,
A first error correction encoding unit that performs error correction encoding processing on the first stream of bitstreams, and a second error correction encoding unit that performs error correction encoding processing of the second stream of bitstreams; A transmission apparatus, wherein a bit stream subjected to correction coding processing is input to the layer mapping unit. The transmission device according to any one of claims 1 to 3,
The transmission apparatus according to claim 1, wherein the first error correction encoding unit and the second error correction encoding unit perform different encoding processes. The transmission apparatus according to any one of claims 1 to 4,
A transmission apparatus characterized in that OFDM modulation is performed by arranging signal points (data symbols) generated by the layer mapping unit on a frequency axis and a time axis. In a receiving apparatus that receives a modulated signal by mapping a plurality of bit streams to one signal point, the signal points are demapped and the obtained bit-specific data is separated into the plurality of bit streams. A hierarchical demapping unit
The plurality of bit streams are subjected to error correction coding processing before mapping,
The hierarchical demapping unit demapping the signal points to obtain the likelihood of each bit; and
A likelihood separation unit that separates the likelihood of each bit into the plurality of bitstreams;
An error correction decoding process is performed on the basis of the likelihood for each series of bitstreams.

Images